1. Field Of The Invention
This invention relates to a tool for sampling fluids from downhole well formations, and more particularly, to a perforate, test and sample tool with a tester valve positioned above a packer and having a bypass means for allowing actuation by annulus pressure of a firing mechanism for guns below the packer.
2. Description Of The Prior Art
Well testing operations are commonly conducted on oil and gas wells in order to determine production potential and to enhance the same if possible. In flow testing a well, a tester valve is lowered into the well on a string of drill pipe above the packer. After the packer is set, the tester valve is opened and closed periodically to determine formation flow, pressure and rapidity of pressure recovery. One such downhole tool which is capable of performing in different modes of operation as a drill pipe tester valve, a circulation valve and a formation tester valve, as well as providing the operator with the ability to displace fluids in the pipe string above the tool with nitrogen or other gas prior to testing or retesting, is disclosed in U.S. Pat. No. 4,633,952 to Ringgenberg, assigned to the assignee of the present invention. This tool is also described in Halliburton Services Sales & Service Catalog No. 43, page 2548 as the Omni.RTM. circulating valve. Another similar circulating valve is disclosed in U. S. Pat. No. 4,657,082 to Ringgenberg, also assigned to the assignee of the present invention. As indicated, the Omni.RTM. circulating valve can be used as a tester valve, but is not adapted for use with pressure actuated time delay firing means for guns below a packer because the valve does not have a bypass which provides communication between the well annulus above the packer and the components of the tool string below the packer.
Preferably, formation testing is carried out by running a tool string into the well bore one time, making the test, and removing the tool string. Tester valves positioned below packers have been utilized to perform such tests, but these devices are relatively complex. Accordingly, there is a need for a simplified testing system. The present invention provides a perforate, test and sample (PTS) tool which can be lowered into a well bore on a tool string including a packer so that the well bore may be closed off prior to actuating perforating guns positioned below the packer. Well annulus pressure must be used to actuate the firing mechanism for the guns, and the present invention includes a tester valve disposed above the packer which has a bypass means for providing fluid communication from the well annulus above the packer to the firing mechanism below the packer. The bypass means is closeable prior to the actual firing due to a time delay in the firing mechanism. The tester valve is basically an upside-down and modified version of the Omni.RTM. circulating valve, so that the bypass means is positioned below the sampling valve means in the tester valve. The tester valve of the present invention is used to fill a relatively small sampling chamber, and thus high flow rates are not necessary. The present invention therefore uses a sliding sleeve valve means rather than a relatively expensive ball valve means.